The invention relates to a device for measuring heart rate information non-invasively, particularly to a heart rate monitor used in connection with physical exercise and sports.
In connection with physical exercise, measurement of heartbeat rate presents an attractive task. The heartbeat rate, i.e. heart rate, provides information e.g. on a person""s exercise intensity, recovery and changes in the physical condition, enabling the relationship between exercise and rest to be monitored and planned in a better way.
Heart rate is measured from a person""s skin on the basis of an electrocardiographic (ECG) signal produced by a heartbeat. Further information on ECG can be found in Human Physiology and Mechanisms of Disease by Guyton, Arthur C., Third Edition, Chapter 13: The Electrocardiogram, W. B. Saunders Company 1982, ISBN 4-7557-0072-8, which is incorporated herein by reference. An electrocardiographic signal is an electromagnetic signal produced by the heartbeat, detected on the body of a person to be measured. The signal is measured using electrodes that at least at two points come into contact with the body. In practice, an electrode nearest to the heart on a polarization vector usually operates as the actual measuring electrode while another electrode provides ground potential, a voltage measured by the measuring electrode being compared to the ground potential as a function of time. Publication U.S. Pat. No. 6,018,677, which is incorporated herein by reference, discloses a method and apparatus for measuring heart rate on the basis of a measured ECG signal. FIG. 3A in patent application GB 2 339 833A filed by the present applicant discloses a prior art solution for positioning electrodes in a electrode belt. According to what has been disclosed in the publication, the electrode belt is placed on the chest while electrodes to be arranged against the chest measure the ECG signal produced by the heartbeat.
As far as user-friendliness is concerned, the prior art solution for measuring heart rate using an electrode belt is not an optimal arrangement for the user. The belt, which is of considerable size, has to be arranged under the user""s shirt, which makes it difficult to arrange and possibly adjust the belt appropriately so as to ensure better measurement results during a physical exercise.
An object of the invention is to provide an improved method and apparatus implementing the method for measuring an electrical heart rate signal on a person""s body. This is achieved by the method to be disclosed in the following. The method is a method for measuring an ECG signal on a person""s skin, in which method a potential difference caused by the ECG signal is measured by means of a first electrode and a second electrode in an electrode structure that come into contact with the person""s skin. In the method, the first electrode is at least partly located on an inner surface of the electrode structure to be arranged around a finger, the inner surface residing against the finger, and the second electrode is located on an outer surface of the electrode structure.
The invention further relates to an electrode structure for measuring an ECG signal on a person""s skin. The electrode structure to be arranged on the person""s finger comprises an inner surface residing against the finger, which inner surface of the electrode structure comprises an inner surface electrode, the electrode structure further comprising an outer surface opposite to the inner surface, which outer surface of the electrode structure comprises an outer surface electrode to be arranged against a point on the person""s skin other than said finger having the electrode structure arranged thereon, the electrode structure being arranged to measure a potential difference caused by the ECG signal between a first electrode and a second electrode.
The invention further relates to a heart rate measuring arrangement for measuring an ECG signal on a person""s skin. The heart rate measuring arrangement comprises an electrode structure to be arranged on the person""s finger and a wrist receiver unit, which electrode structure comprises an inner surface residing against the skin on the finger, the inner surface of the electrode structure comprising an inner surface electrode, the electrode structure further comprising an outer surface opposite to the inner surface, the outer surface of the electrode structure comprising an outer surface electrode to be arranged against a point on the person""s skin other than said finger having the electrode structure arranged thereon, the electrode structure comprising ECG processing means connected to the electrodes for measuring a potential difference caused by the ECG signal in a first electrode and a second electrode and for producing heart rate information on the basis of the measured potential difference, the electrode structure further comprising a transmitter for transmitting heart rate information to the wrist receiver comprising a receiver for receiving the heart rate information transmitted from the electrode structure, the wrist receiver further comprising a display for displaying the heart rate information.
Preferred embodiments of the invention are disclosed in the dependent claims.
The invention thus relates to a method and apparatus implementing the method for measuring a heart rate signal on a person""s skin. The electrode structure to be used in a solution of the invention is to be arranged at least partly around the user""s finger. In an embodiment, the electrode structure comprises two open ends, enabling the electrode structure to be slid over and around a considerable section of the finger. In an embodiment, the electrode structure comprises one closed end, in which case the electrode structure is slid over the finger such that the closed end resides on the fingertip. Preferably, the electrode structure is then shaped like a cylinder, i.e. it has a spherical cross-section. It is obvious that the electrode structure is not necessarily exactly cylindrical but may be e.g. conical. In a conical structure, for example the cross-section of the end of the electrode structure located farther away from the fingertip is larger than that of the end located closer to the fingertip. It is obvious that the electrode structure may also have a cross-section shaped like a square, rectangle, ellipse or the like.
On its inner surface residing against a finger, the electrode structure comprises an inner surface electrode. The electrode structure also comprises an outer surface, which is a surface with no contact with the skin on the finger having the electrode structure arranged thereon. On its outer surface, the electrode structure comprises an outer surface electrode to be arranged against a point on the person""s skin other than said finger having the electrode structure arranged thereon. It is obvious to one skilled in the art that the invention is not restricted to the electrode structure only comprising one inner surface electrode and one outer surface electrode but there may be more than one such electrode. The inner surface and the outer surface of the electrode structure are electrically isolated from each other to enable a potential difference between the electrodes to be measured. In order to ensure optimal measurement of a heart rate signal, the outer surface electrode is set against a point on the skin located on a side of an electrical vector formed by the heartbeat other than the one on which said finger resides, which enables an ECG signal to be detected. During measurement, the outer surface electrode is placed e.g. against the user""s forehead or finger in a hand other than the one having the electrode structure arranged thereon. In a preferred embodiment of the invention, the electrode structure comprises a control unit for determining a point in time at which the electrodes are brought into contact with the user""s skin. The procedure used therein preferably employs impedance measuring or pressure measuring techniques.
Preferably, the electrodes in the electrode structure are connected to a central processing unit, which, on the basis of the heart rate signals measured by the electrodes, estimates points in time for detected heartbeats and further, on the basis of the detected points in time for heartbeats, calculates the heart rate. The central processing unit is located e.g. in a watch-like device worn on the user""s wrist, such as a heart rate monitor or a wrist computer. Information is then transmitted between the electrode structure and the heart rate monitor using the known methods, e.g. optically, electromagnetically or through a transfer circuit. In such an embodiment, a display for displaying heart rate information is preferably also located in the wrist receiver. In a preferred embodiment of the invention, all necessary parts in the apparatus and procedures performed by such parts to measure, process and display heart rate information are provided and carried out in the electrode structure worn on the finger. The heart rate information is then preferably displayed by a display on the outer surface of the electrode structure, such as a liquid crystal display. It is obvious that in the case of a separate receiver unit, the display of the electrode structure and the display of the heart rate monitor are not mutually exclusive but both device units or only one such unit may comprise a display.
An advantage of the invention is that compared to the known solutions, the electrode structure is hardly noticeable and more user-friendly.